β3 integrin subunit specific polypeptides, cDNAs which encode these polypeptides and method of producing these polypeptides

ABSTRACT

β 3  integrin subunit specific polypeptides, cDNAs which encode these polypeptides and methods of producing these polypeptides are provided.

This invention was made in the course of research sponsored by the National Institutes of Health. The U.S. Government may have certain rights in this invention.

BACKGROUND OF THE INVENTION

Integrins are heterodimeric cell surface adhesion receptors which play an important role in normal and pathological processes including hemostasis and thrombosis. These receptors contain both an α and a β subunit. The integrin dimer has a cytoplasmic domain associated with the cytoskeleton. Thus, integrins form a critical connection between the extracellular matrix and the internal structural elements of a cell.

The most abundant integrin on platelets is α_(IIb) β₃. α_(IIb) and β₃ are type I transmembrane glycoproteins that contain 1008 and 762 amino acids, respectively. These glycoproteins are complexed together in membranes as non-covalent heterodimers. More than 95% of each subunit is extracellular; each has a single transmembrane domain and a short cytoplasmic tail (20 amino acids in α_(IIb) and 47 amino acids in β₃).

α_(IIb) β₃ mediates platelet aggregation as well as platelet adhesion and spreading on extracellular matrices. The affinity of this integrin for its extracellular ligands, arginine-glycine-aspartic acid (RDG)-containing ligands such as fibrinogen, von Willebrand factor (vWf), fibronectin and vitronectin, is regulated by the cell by a process known as "inside-out" signaling. Binding of a ligand such as fibrinogen to α_(IIb) β₃ initiates a cascade of signaling reactions necessary for full platelet adhesion. This process is referred to as "outside-in" signaling.

This regulation by the cell is an important feature of the ligand-receptor interaction. Platelets normally circulate in a resting state in which the apparent affinity of α_(IIb) β₃ for ligands is low. When platelets enter a vascular wound or encounter a physiological agonist, such as thrombin or ADP, or an activator of protein kinase C, such as phorbol myristate acetate (PMA), affinity for the receptor is rapidly increased resulting in ligand binding and platelet aggregation. (Bennett, J. S. and Vilaire, G., J. Clin. Invest. 1979, 64, 1393). Platelet aggregation is initiated by the bridging of α_(IIb) β₃ complexes on adjacent platelets by fibrinogen or vWf. This increase in affinity can be prevented or reversed by addition of compounds that result in increased amounts of intracellular cyclic AMP or cyclic GMP such as prostaglandin I₂ or nitric oxide, respectively. (Graber, S. E. and Hawiger, J., J. Biol. Chem. 1982, 257, 14606).

Platelet activation induces a conformational change in α_(IIb) β₃, exposing a ligand-binding site that is likely to be composed of several discontinuous regions in the amino-terminal portions of both the α_(IIb) and the β₃ subunits. (Sims et al. J Biol Chem 1991, 266, 7345-7352; Plow et al. Semin Thromb Hemost 1992, 18, 324-332). Receptor affinity is believed to be regulated through cytoplasmic tails of the α_(IIb) β₃. Substitution of the cytoplasmic domains of α_(IIb) β₃ with those of α₅ β₁ in Chinese hamster ovary cells conferred an energy-dependent high affinity state on the extracellular portions of α_(IIb) β₃. (O'Toole et al. J Cell Biol 1994, 124, 1047-1059). It is believed that intracellular signals generated by an agonist or antagonist result in modifications in the cytoplasmic domain of the α_(IIb) and β₃ subunits. These modifications lead to changes in the extracellular portion of the receptor that increase or decrease accessibility of the ligand binding site. (Ginsberg et al. Curr. Opin. Cell. Biol. 1992, 4, 766). The study of recombinant forms of α_(IIb) β₃ have shown that the affinity state of the fibrinogen receptor is influenced by sequences in the receptor's cytoplasmic tails in a cell type specific and energy-dependent manner. Thus, it has been suggested that specific cellular proteins interact with the tails and regulate receptor function. (O'Toole et al. J Cell Biol 1994, 124, 1047-1059).

Only a few intracellular proteins which interact with the cytoplasmic domains or tails of the α_(II) and β₃ subunits and regulate inside-out and outside-in signaling have been identified. Otey et al.(J Cell Biol 1990, 111, 721-729) demonstrated that α-actinin binds to the cytoplasmic domain of the β subunit of intact integrins from both the β₁ and β₃ subfamilies. They have also attempted to identify the binding site for α-actinin within the β₁ integrin cytoplasmic domain. (Otey et al. J. Biol. Chem. 1993, 268, 21193-21197).

Human cDNAs have now been identified which express β₃ integrin subunit specific polypeptides.

SUMMARY OF THE INVENTION

An object of the invention is to provide a β₃ integrin subunit specific polypeptide.

Another object of the invention is to provide a cDNA sequence which encodes a β₃ integrin subunit specific polypeptide.

Another object of the present invention is to provide an expression vector which comprises a DNA sequence which encodes a β₃ integrin subunit specific polypeptide. Cell lines transfected with this expression vector are also provided.

Another object of the present invention is to provide a method of making a β₃ integrin specific polypeptide by culturing a cell transfected with an expression vector containing a DNA which encodes a β₃ integrin specific polypeptide and recovering this polypeptide from the cell.

DETAILED DESCRIPTION OF THE INVENTION

β₃ integrin subunit specific polypeptides, cDNAs which encode these polypeptides and methods of producing these polypeptides have now been found. These β₃ integrin subunit specific polypeptides of the present invention interact specifically with the β₃ subunit of integrin in vivo and are believed to regulate the adhesive and signaling functions of β₃ integrins. For the purpose of this invention a "β₃ integrin subunit specific polypeptide" is meant to include any polypeptide which interacts specifically with the β₃ integrin cytoplasmic tail encoded by a DNA sequence comprising a clone. By specifically it is meant that the polypeptides of the present invention interact preferentially with the β₃ integrin subunit as compared to the β₂ or α_(IIb) subunits. Specific interaction is demonstrated in vitro using, for example, a yeast system and a standard β-galactosidase assay suitable for analysis of yeast lysates.

A human cDNA clone (hereinafter referred to as "clone 28") has now been obtained through molecular cloning using a yeast two hybrid system. Clone 28, which was isolated from an Epstein Barr virus transformed human B-cell library, contains 723 base pairs (SEQ ID NO: 1) and encodes a β₃ integrin subunit specific polypeptide. cDNA similar to clone 28 have now been identified in a number of human tissues.

Clone 28 encodes a 95 amino acid β₃ integrin subunit specific polypeptide (SEQ ID NO: 2). In a preferred embodiment, the clone comprises clone 28 (SEQ ID NO: 1) which encodes a polypeptide, SEQ ID NO: 2. Specificity of the polypeptide for the β₃ integrin subunit can be demonstrated by several techniques. For example, specific interaction of SEQ ID NO:2 was demonstrated in the intracellular environment of a strain of yeast, Saccharomyces cervisiae. In the yeast system, clone 28 cDNA was fused to the 3' end of the activation domain of the GAL4 transcriptional activator. Interaction of the expressed fusion protein with a second fusion protein comprising the GAL4 binding domain and the β₃ cytoplasmic domain was then assessed by the transactivation of two reporter genes, HIS3 and lacZ, under the control of GAL 4. This protein-protein interaction was found to be a specific interaction meaning that there is no interaction of the polypeptide encoded by clone 28 with several unrelated control proteins also fused to the GAL4 DNA binding domain. Further, it was demonstrated that interaction of the clone 28-derived polypeptide with the β₃ cytoplasmic tail is decreased by mutating the β₃ tail. For example, mutation of a serine to a proline at amino acid residue 752 of the β₃ tail resulted in a 70% reduction in the interaction of the clone 28-derived polypeptide with the β₃ cytoplasmic tail. The strength of these binding interactions was measured using a quantitative β-galactosidase assay suitable for analysis of yeast lysates. (Ausubel et al., Current Protocols in Molecular Biology, Wiley, New York 1990). This mutation of the β₃ cytoplasmic tail is known to be associated with defective adhesive and signaling functions of the integrin, both in a patient and in a heterologous system expressing recombinant integrin. (Chen et al. Proc Natl Acad Sci USA 1992, 89, 10169-10173; O'Toole et al. J. Cell Biol 1994, 124, 1047-1059).

Several forms of clone 28-related mRNA or cDNA have been found in human tissues. In Northern blot studies performed using standard methods as described by Sambrook et al., (Molecular Cloning, Cold Spring Harbor Laboratory Press, 2nd edition, 1989), mRNA of approximately 1.1 to 1.2 kb was found in all human tissues examined including colon, blood leukocytes, prostate, testes, spleen, thymus and small intestine. In addition, using standard and 5'RACE PCR methods (Schuster et al. Focus 1992, 14, 46), larger clones encoding at least two different forms of cDNA have been identified in human cDNA libraries prepared from B lymphocyte, placenta and brain and by RT-PCR of an enriched preparation of platelets. One of these forms containing approximately 897 basepairs (SEQ ID NO: 3) encodes a β₃ integrin subunit specific polypeptide of the invention comprising about 111 amino acids (SEQ ID NO: 4).

The β₃ integrin subunit specific polypeptides of the present invention can be used in a variety of applications routine to one of skill in the art based upon this disclosure. Specifically, the β₃ integrin subunit specific polypeptides of the present invention can be used as immunogens to raise antibodies which are specific to the cloned peptides. Various procedures known in the art may be used for the production of antibodies to β₃ integrin subunit specific polypeptides. Such antibodies include, but are not limited to, polyclonal, monoclonal, chimeric, single chain, Fab fragments and an Fab expression library. For the production of antibodies, various host animals including, but not limited to rabbits, mice, and rats, are injected with a β₃ integrin subunit specific polypeptide. In one embodiment, the polypeptide or a fragment of the polypeptide capable of specific immunoactivity is conjugated to an immunogenic carrier. Adjuvants may also be administered in conjunction with the polypeptide to increase the immunologic response of the host animal. Examples of adjuvants which may be used include, but are not limited to, complete and incomplete Freund's, mineral gels such as aluminum hydroxide, surface active substances such as lysolecithin, pluronic polyols, polyanions, peptides, oil emulsions, keyhole limpet hemocyanin, and dinitrophenol.

Monoclonal antibodies to β₃ integrin subunit specific polypeptides of the present invention can be prepared using any technique which provides for the production of antibodies by continuous cell line in culture. Such techniques are well known to those of skill in the art and include, but are not limited to, the hybridoma technology originally described by Kohler and Milstein (Nature 1975, 256,495-497), the human B-cell hybridoma technique described by Kosbor et al. (Immunology Today 1983, 4, 72) and the EBV-hybridoma technique described by Cole et al. (Monoclonal Antibodies and Cancer Therapy, Alan R. Liss, Inc., pp 77-96).

Antibodies immunoreactive to the polypeptides of the present invention can then be used to screen for the presence and subcellular distribution of similar polypeptides in biological samples. In addition, monoclonal antibodies specific to the β₃ integrin subunit specific polypeptides of the present invention can be used as therapeutics. A monoclonal antibody directed against the platelet glycoprotein IIb/IIIa receptor is presently in clinical trials in high risk coronary angioplasty patients. (The Epic Investigator, New Engl J Med 1994, 330, 956-961).

The β₃ integrin subunit specific polypeptides can also serve as antigens useful in solid phase assays measuring the presence of antibodies which immunoreact with the claimed peptides. Solid phase competition assays can be used to measure immunological quantities of clone 28-related antigen in biological samples. This determination is not only useful in facilitating the complete characterization of the cellular function or functions of the β₃ integrin subunit specific polypeptides of the present inventions, but can also be used to identify patients with abnormal amounts of these proteins.

β₃ integrin subunit specific polypeptides of the present invention can also be used as capture reagents in affinity chromatography for the detection of proteins in addition to the β₃ integrin cytoplasmic domain that may become engaged in an intracellular macromolecular complex with integrins and to regulate adhesion receptor function. There is increasing evidence that such "signalling organelles" exist; however, there compositions are presently undetermined. (Sastry, S. K. and A. F. Horwitz, Curr Opin Cell Biol 1993, 5, 819-831). Affinity chromatography using β₃ integrin subunit specific polypeptides as the capture agent will facilitate characterization of these complexes.

In addition, these β₃ integrin subunit specific polypeptides are useful as reagents in an assay to identify candidate molecules which effect the interaction of the β₃ subunit and the cloned protein. Compounds that specifically block integrin activation without affecting other platelet responses have not yet been discovered. The screening process for such compounds is more complicated than that for inhibitors of ligand binding. For example, identification of inhibition of ligand binding has been facilitated by the finding that the RGD sequence is an integrin-recognition motif common to most α_(IIb) β₃ ligands. (Plow, E. F. et al., Proc. Natl. Acad. Sci. USA 1985, 82, 8057) In contrast, the structural requirements for specific inhibition of activation of α_(IIb) β₃ are unknown. Furthermore, studies of ligand binding to α_(IIb) β₃ have been facilitated by the use of paraformaldehyde-fixed platelets and even activated forms of purified or recombinant α_(IIb) β₃ (Shattil, J. S. et al., Blood 1987, 70, 307; Alig, L. et al., J. Med. Chem. 1992, 35, 4393; O'Toole, T. E. et al., J. Cell. Biol. 1994, 124, 1047). However, these forms of the receptor cannot be used to search for intracellular inhibitors of integrin activation because dynamic regulation of α_(IIb) β₃ by agonists has been observed only in the intact, metabolically active platelet (Smyth, S. S. and Parise, L. V. Biochem. J. 1993, 292, 749). Use of the polypeptides of the present invention, however, can be used with permeabilized active platelets to screen potential integrin inhibitors and activators which compete with these β₃ integrin subunit specific polypeptides to interact specifically with α_(IIb) β₃ integrin.

These β₃ integrin subunit specific polypeptides are also useful in acellular in vitro binding assays wherein alteration by a compound in the binding of these β₃ integrin subunit specific polypeptides to a β₃ integrin cytoplasmic tail is determined. Acellular assays are extremely useful in screening sizable numbers of compounds since these assays are cost effective and easier to perform than assays employing living cells. Upon disclosure of the polypeptides of the present invention, the development of these assays would be routine to the skilled artisan. In such assays, either the β₃ integrin subunit specific polypeptide or the β₃ integrin cytoplasmic tail is labeled. Such labels include, but are not limited to, radiolabels, antibodies, and fluorescent or ultraviolet tags. Binding of a β₃ integrin subunit specific polypeptide to the β₃ integrin cytoplasmic tail is first determined in the absence of any test compound. Compounds to be tested are then added to the assay to determine whether such compounds alter this interaction.

Compounds that inhibit activation of, or ligand binding to, α_(IIb) β₃ are therapeutically useful in conditions associated with occlusive platelet thrombi, such as unstable angina, acute myocardial infarction, abrupt vascular occlusion after coronary angioplasty, or transient ischemic attacks. In fact, antibody, peptidic and non-peptidic inhibitors of fibrinogen binding to α_(IIb) β₃ are currently undergoing clinical trials (The Epic Investigators, New Engl. J. Med. 1994, 330, 956). The effectiveness of these compounds as platelet aggregation inhibitors appears to be directly related to their ability to occupy α_(IIb) β₃ and block ligand binding (Coller, B. S., Annu. Rev. Med. 1992, 43, 171).

Another advantage of the invention is its usefulness in screening for compounds that activate platelet integrin α_(IIb) β₃ ligand binding. These compounds can be used in conditions associated with impaired blood coagulation such as in liver diseases which cause a reduction in clotting factors. The administration of a platelet integrin α_(IIb) β₃ activator in such situations is useful to improve blood clotting under conditions of reduced availability of clotting factors.

In addition to providing a means for expressing β₃ integrin subunit specific polypeptides, the cDNAs of the present invention can also be used to clone the human chromosomal gene. Once a cDNA for a particular gene has been isolated it is within the routine skill of those in the art to clone the chromosomal gene. This is known as the genomic clone. Total chromosomal DNA is isolated and purified from any human tissue. The DNA is then cut into fairly large fragments by restriction enzymes, ligated into a suitable vector and then transformed into E. coli. Colonies are then allowed to form. A cDNA of the present invention is used as a probe for these colonies. The cDNA is first purified and then radiolabeled by nick translation. It is then contacted with the colonies. The cDNA only hybridizes with colonies containing the chromosomal gene of interest. The chromosomal gene is useful in a variety of assays including diagnosis of mutations in the gene. Integrins play an important role in normal and pathological processes including hemostasis and thrombosis. Such processes control normal cardiovascular function. Mutations in the gene which expresses integrins could result in abnormalities in these processes. Thus, genetic analysis may be used for the early diagnosis of patients at high risk for cardiovascular abnormalities. Early diagnosis and treatment of such abnormalities is useful in preventing myocardial infarction, strokes and other cardiovascular related maladies.

The following nonlimiting examples are provided to further illustrate the present invention.

EXAMPLES Example 1

Identification and isolation of clone 28

Clone 28 was identified as a β₃ integrin subunit specific polypeptide using the yeast two-hybrid system as described by Fields et al. (Nature 1989, 340, 245). The GAL4 binding domain in the yeast vector, pGBT9 (Clontech, Palo Alto, Calif.), was fused at its 3' end to the β₃ cytoplasmic domain. An EBV-transformed B cell cDNA library was obtained and fused to the 3' end of the GAL4 activation domain in the yeast vector, pACT (Elledge et al. Proc Natl Acad Sci USA 1991, 88, 1731). The yeast strain Y-190 was sequentially transformed with these vectors and the yeast grown under conditions or Trp, Leu and His auxotrophy. Yeast colonies able to overcome this auxotrophy were then screened for expression of β-galactosidase activity on filter lifts and individual transformants were subsequently analyzed by quantitative β-galactosidase activity. Quantitative β-galactosidase activity correlates with the strength of the interaction in yeast between the β₃ cytoplasmic domain and an interacting polypeptide whose cDNA was originally present in the B cell library. Of 1.5 million independent yeast transformants in the initial library screen, five were strikingly positive for β-galactosidase activity. All five were identical to clone 28 (SEQ ID NO:1).

Example 2

Expression of β₃ integrin subunit specific polypeptide

SEQ ID NO: 2, the polypeptide encoded by clone 28, was expressed as a GST fusion protein in E. coli and then cleaved from the GST. The polypeptide was then purified in accordance with procedures described by Frangione et al. Anal Biochem 1993, 210, 179. The purified polypeptide was used in the preparation of monoclonal and polyclonal antibodies.

Example 3

Determination of specificity to the β₃ subunit

The specificity of the polypeptides of the present invention for the β₃ cytoplasmic domain was determined in yeast using the quantitative β-galactosidase assay. Results from a series of these assays demonstrate that SEQ ID NO: 2 and SEQ ID NO: 4 bind avidly to the β₃ cytoplasmic domain. In sharp contrast, these polypeptides did not bind significantly to either the integrin β₁ or β₂ cytoplasmic domains, nor did they bind to irrelevant proteins fused to the GAL4 binding domain. In addition, the β₃ cytoplasmic domain does not bind to nonspecific fusion proteins such as SV40 large T antigen or the integrin α_(IIb) subunit. Accordingly, these experiments establish the consistency and specificity of the interaction of the polypeptides of the present invention and the β₃ cytoplasmic domain.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 4                                                   (2) INFORMATION FOR SEQ ID NO: 1:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 723                                                                (B) TYPE: Nucleic Acid                                                         (C) STRANDEDNESS: Single                                                       (D) TOPOLOGY: Linear                                                           (iv) ANTI-SENSE: NO                                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 1:                                       GGCCACGAAGGCCCAAAAATCACAAGGAAGAAAAGTGTTATAACTTATTC50                           TCCAACAACTGGAACTTGTCAAATGAGTCTATTTGCTTCTCCCACAAGTT100                          CTGAAGAGCAAAAGCACAGAAATGGACTATCAAATGAAAAGAGAAAAAAA150                          TTGAATCACCCCAGTTTAACTGAAAGCAAAGAATCTACAACAAAAGACAA200                          TGATGAATTCATGATGTTGCTATCAAAAGTTGAGAAATTGTCAGAAGAAA250                          TCATGGAGATAATGCAAAATTTAAGTAGTATACAGTGACAAAAGTGAATA300                          AACAAAAACTGTTTGAAAAGAGTACAGGACTTCCTCACAAAGCATCACGT350                          CATCTTGACAGCTATGAATTCCTTAAAGCCATTTTAAACTGAGGCATTAA400                          GAAGAAATGCACTCACCATGAGCACCAACTTCTGCATCTGCCTGATCATA450                          TTTAAAGGAACAGAGAAATATTTGTAATTAATCTGCCCAGTAAATACCAG500                          CTCGTAGCAGTTGGCAGGTGCATGTCTAGATAAAATTTCTTGCAGCTAAT550                          TTAAACTTTCTAACCGCACCAGTAGATAATCTCAATGTAAATAATACATT600                          TCTTCTTGGCTCTTTAATGTAAGCCAACATGGAGAGGAAGATCTTGACTT650                          ATATTCTGTACCACATACACTTCTGTGGACTTTTAGCATTTGTGGGTAGA700                          CTTAATGGCCTTCGTGGCCTCGA723                                                     (2) INFORMATION FOR SEQ ID NO: 2:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 95                                                                 (B) TYPE: Amino Acid                                                           (D) TOPOLOGY: Linear                                                           (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 2:                                       GLYHISGLUGLYPROLYSILETHRARGLYSLYSSERVALILETHR                                  51015                                                                          TYRSERPROTHRTHRGLYTHRCYSGLNMETSERLEUPHEALASER                                  202530                                                                         PROTHRSERSERGLUGLUGLNLYSHISARGASNGLYLEUSERASN                                  354045                                                                         GLULYSARGLYSLYSLEUASNHISPROSERLEUTHRGLUSERLYS                                  505560                                                                         GLUSERTHRTHRLYSASPASNASPGLUPHEMETMETLEULEUSER                                  657075                                                                         LYSVALGLULYSLEUSERGLUGLUILEMETGLUILEMETGLNASN                                  808590                                                                         LEUSERSERILEGLN                                                                95                                                                             (2) INFORMATION FOR SEQ ID NO: 3:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 897                                                                (B) TYPE: Nucleic Acid                                                         (C) STRANDEDNESS: Single                                                       (D) TOPOLOGY: Linear                                                           (iv) ANTI-SENSE: NO                                                            (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 3:                                       CTGGTTCGGCCCACCTCTGAAGGTTCCAGAATCGATAGTGAATTCGTGGT50                           TTCCTTTGGCGGATTTTCTGTTTTCGGAAGTTGCTGGGTTCGTTTTATTC100                          AGCGGCAGTGGTGCTTTCCCGAATCTCAGAATGCCTGTTAAAAGATCACT150                          GAAGTTGGATGGTCTGTTAGAAGAAAATTCATTTGATCCTTCAAAAATCA200                          CAAGGAAGAAAAGTGTTATAACTTATTCTCCAACAACTGGAACTTGTCAA250                          ATGAGTCTATTTGCTTCTCCCACAAGTTCTGAAGAGCAAAAGCACAGAAA300                          TGGACTATCAAATGAAAAGAGAAAAAAATTGAATCACCCCAGTTTAACTG350                          AAAGCAAAGAATCTACAACAAAAGACAATGATGAATTCATGATGTTGCTA400                          TCAAAAGTTGAGAAATTGTCAGAAGAAATCATGGAGATAATGCAAAATTT450                          AAGTAGTATACAGTGACAAAAGTGAATAAACAAAAACTGTTTGAAAAGAG500                          TACAGGACTTCCTCACAAAGCATCACGTCATCTTGACAGCTATGAATTCC550                          TTAAAGCCATTTTAAACTGAGGCATTAAGAAGAAATGCACTCACCATGAG600                          CACCAACTTCTGCATCTGCCTGATCATATTTAAAGGAACAGAGAAATATT650                          TGTAATTAATCTGCCCAGTAAATACCAGCTCGTAGCAGTTGGCAGGTGCA700                          TGTCTAGATAAAATTTCTTGCAGCTAATTTAAACTTTCTACACGCACCAG750                          TAGATAATCTCAATGTAAATAATACATTTCTTCTTGGCTCTTTAATGTAA800                          GCCAACATGGAGAGGAAGATCTTGACTTATATTCTGTACCACATACACTT850                          CTGTGGACTTTTAGCATTTGTGGGTAGACTTAATGGCCTTCGTGGCC897                             (2) INFORMATION FOR SEQ ID NO: 4:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 111                                                                (B) TYPE: Amino Acid                                                           (D) TOPOLOGY: Linear                                                           (xi) SEQUENCE DESCRIPTION: SEQ ID NO: 4:                                       MetProValLysArgSerLeuLysLeuAspGlyLeuLeuGluGlu                                  51015                                                                          AsnSerPheAspProSerLysIleThrArgLysLysSerValIle                                  202530                                                                         ThrTyrSerProThrThrGlyThrCysGlnMetSerLeuPheAla                                  354045                                                                         SerProThrSerSerGluGluGlnLysHisArgAsnGlyLeuSer                                  505560                                                                         AsnGluLysArgLysLysLeuAsnHisProSerLeuThrGluSer                                  657075                                                                         LysGluSerThrThrLysAspAsnAspGluPheMetMetLeuLeu                                  808590                                                                         SerLysValGluLysLeuSerGluGluIleMetGluIleMetGln                                  95100105                                                                       AsnLeuSerSerIleGln                                                             110                                                                            __________________________________________________________________________ 

What is claimed is:
 1. A purified β₃ integrin subunit specific polypeptide comprising SEQ ID NO: 2 or
 4. 2. A purified β₃ integrin subunit specific polypeptide expressed from a human cDNA comprising SEQ ID NO: 1 or
 3. 